Alloy steels



j uses in the arts.

Patented Apr. 18, 1939 UNITED. STATES? PATENT OFFICE Chicago, 111.; saidUnited States Steel Grossmann assignor to Corporation, New York,

N. Y., a corporation of New Jersey No Drawing. Original applicationSeptember 14, 1935, Serial No. 40,655. Divided and this applicationNovember 2, 1936, Serial'No. 108,899

2 Claims.

The present invention relates to alloy steels.

This application is a division of the application for. United StatesLetters Patent filed on September 14, 1935, by the present applicants,for improvements in Alloy steels, which application bears Serial No.40,655.

In the strict sense, steel may be said to be an alloy of iron andcarbon. However, in a metallurgical sense, in which the term is used inthis specification, an alloy steel is steel (that is-iron and carbon)alloyed with another chemical element or other chemical elements.

An object of the present invention is to produce an alloy steel which iswell adapted to resist failure by fatigue, especially for use in highlystressed parts, such as springs.

A further object is to produce an alloy steel for general purposes whichinvolves no special equipment in its manufacture and which has improvedcharacteristics over steel as heretofore known and used. I

A further object is to provide a steel well adapted for use incushioning springs, which steel will effectually resist deterioration inservice.

A further object is to provide an alloy steel in which thecharacteristics of vanadium are utilized to advantage in the manufactureof alloy steels.

A further object is to provide an improved steel well adapted to meetthe needs of commercial operation.

Further objects will appear as the description proceeds.

The present invention contemplates the accomplishment of the objectsabove referred to by providing a shallow hardening alloy steel. To theskilled steel manufacturer the term shallow hardening alloy steel has adefinite significance, meaning a steel which, when heated to above itscritical temperature and then cooled, has a relatively pronouncedtendency to change rapidly from the austenitic to the pearlitic type ofinternal structure. Steel of fine grain structure tends to be shallowhardening, though of .course certain alloy steels, even though they befine grained, may not be shallow hardening in comparison with the steelsfor which invention is claimed herein. Of course it is possible to produce shallow hardening steel by using a very restricted amount ofcarbon, and such steel has its The present invention is limited to-steels in which the carbon content is equal to or greater than 45% byweight.

In defining the degree of shallow hardening contemplated in the presentinvention it may be observed that certain alloy steels, as for examplenickel chromium steel, have characteristics differing from steelscontemplated in the present invention.- As is well known, alloy steelsas ordinarily known to metallurgists will, when heated to a temperatureof say 1600 deg. F., form austenite, which is understood bymetallurgists to be a solution of carbon in iron. As the steel is cooledfrom the temperature referred to, the structure changes, and when thesteel reaches the neighborhood of about 900 deg. F. there is a tendencyto form pearlite, which is a tough substance of low hardness. In thecase of most alloy steels as now known and used, as for example thenickel chromium steel above referred to, the length of time in thetemperature zone in the neighborhood of 900 deg. F. required for theformation of pearlite is in the neighborhood of 20 seconds. Thetemperature zone referred to may range from 1050 to 850 deg. F. In thecase of the alloy steels forming the subject matter of the presentinvention, the period of time required in the 900 deg. zone referred tois in the neighborhood of 8 seconds. Considering a body of steel whichhas been heated to say about 1600 deg. F. and quenched in water, it willbe readily understood that in the case of nickel chromium steel or thelike the period of dwell in the 900 deg. zone referred to may be tooshort to form pearlite, but said period of dwell may be ample for theformation of pearlite in the composition of shallow hardening steels. Inother words, using the example above referred to, the period of time inwhich the center of the member under test is in the temperature zone of900 deg. F. above referred to may be less than 20 seconds but more than8 seconds. In the event that pearlite has not formed in the quenchingoperation, the alloy steel, upon further cooling, will form martensite,which is a hard material. In the event that pearlite has formed in thecenter of the member under test in the quenching operation, thispearlite will retain its identity when the member under test has cooledto atmospheric temperature. The above example illustrates a measurewhich may be applied to define the degree of hardenability contemplatedin the present invention. For convenience, the measure of hardenabilitymay be expressed in connection with an alloy steel bar. The presentinvention contemplates a composition of alloy steel such that when acylindrical bar of 1 inches or more in diameter of homogeneouscomposition is heated to a temperature of approximately 1600 deg. F. andthen quenched in still water at room temperature, the material at theaxis of said bar will, upon cooling to room temperature,

have a Rockwell hardness of not more than,

' 1 inch or more in diameter of homogeneous composition is heated to atemperature of approximately 1600 deg. F. and then quenched instill oilat room temperature, the material at the axis of said bar will have aRockwell hardness of not more'than 50C.

It will be understood, of course, that the references immediately abovemade to bars of specified diameters are merely for convenience ofdefinition of one property of these steels. The steels, of course, areuseful in members of all dimensions including small sections in whichthe steels harden through to their axes or midsec' tions.

In carrying out the present invention it is contemplated to use in themanufacture of the improved alloy steel a predominating amount ofvanadium either with or without other shallow hardening elements.correspondingly, the present invention contemplates a relatively lowamount of the deep hardening elements (such for example as manganese,chromium and/or nickel). The relative terms referred to in the precedingsentence have reference to the functions of the alloying elementsreferred to as commonly used in alloy steels in common use today.

Proceeding to a more specific definition of alloying elementscontemplated in the present invention, the following observations may bemade:

Since vanadium reaches its full effectiveness at approximately .15%-.2%by weight, a predominating amount of vanadium in the alloy steelaccording to the present invention would be approximately .075%-.2% byweight.

On the other hand, chromium may be said to have its greatesteffectiveness at about 1.5% by weight, so that a predominating amount ofchromium would be about .'75%-1.5%.

Since manganese reaches its maximum effectiveness at about 2% by weight,a predominating amount of manganese would be about l.25%-2% by weight 7Since nickel reaches its full effectiveness at about 3% to 4%,, apredominating amount of nickel would be about 1%-4% by weight.

Therefore, expressing the purpose of the pres ent invention in otherlanguage, it may be said that the present invention contemplates the useof vanadium in the amount of .075%.2% by weight, said element being usedwithout chromium or manganese if preferred; or, if chromium be used,then with less than .75%'-by weight of chromium; or, if manganese beused,then;w'ith less than 1.25% of manganese. Expressed in still otherlanguage, certain advantages of the present invention will be had if theshallow hardening element (vanadium) is used to a percentage'equal 'toat least 50% of its fully effective amount in is by reference to the"critical cooling rate of the materials. Critical cooling rate'of steelsmay be defined as that rate above which a steel will harden in thecooling process and below which a steel will not harden. When the termharden is used in this connection it is intended to convey the meaningthat the material of the steel becomes the hard material martensite. Thepresent invention contemplates steels which when quenched in a quenchingmedium at atmospheric temperatures will just harden if it passes 1325deg. F. at a rate above 50 deg. per second but below 150 deg. persecond.

Those skilled in the art will understand that manganese is usuallypresent in the manufacture of steel to the extent of about .2 %-.5% byweight, since manganese is commonly used as a deoxidizer in steelmaking; and for the same reason silicon is usually present in amounts ofabout .2%.

' Proceeding now to a still more specific recitation of analysis ofsteel falling within the scope of the present invention, the followingexample may be recited:

Per cent Carbon from .85 to Manganese from .20 to .50 Silicon from .10to .35 Chromium from .20 to .50 Vanadium from .075 to .20

Balance largely iron with traces of impurities.

It will be understood, of course, that the analysis above noted isillustrative only, and the objects of the present invention may berealized by proper balancing of shallow hardening elements against deephardening elements. For example, the carbon may vary from .30% to 1%;

the manganese may vary from .40% to 1.25%; the

chromium may vary from 0 to .75%; the vanadium may vary from .075% to.20%. A choice of the elements referred to to provide a shallowhardening steel meeting the tests recited in this specification willfall within the scope of this invention.

Anyone familiar with the manufacture of alloy steels has readilyavailable to him information as to the constituents and the amountsthereof which must be used in producing the steels havgrain size as usedin this specification means 1 from #5 to #8 on the ASTM chart of grainsizes. This may be further explained as meaning more than12 grains persquare inch when examined at r a magnification of diameters. The fact iswell known that fine grain size tends to shallow hardening; It is alsowell known that very fine grains, particularly #7 and #8, according tothe ASTM chart, exhibit structural features known as abnormality,meaning thereby a particular distribution of the iron carbide (thatiscementite) observed in the carburizing test (McQuaid-Ehn carburizingtest), which test is used in determining grain size.

As is well known, the usual method of discover ing the austenite grainsize of the steel is to carburize said steel at about 1700 deg. F. forabout eight hours. The carbon absorbed in this carburizing operationwill upon cooling arrange itself at the boundaries of the austenitegrains and so outline them, thus making it possible to determine thesize of these austenite grains. In coarsegrained steels this carbon(which is usually present in the form of iron carbide or 'cementite)arranges itself in continuous layers or envelopes which completely andclearly outline the austenite grains. In very fine-grained steels,however, the iron carbide coalesces into separate particles, so that thegrain boundaries are not outlined continuously. This latter condition ofthe iron carbide (cementite), associated with a small amount of ferritein its immediate neighborhood, is often termed divorcement of the ironcarbide or cementite and is commonly known as abnormality. Divorcementof the cementite or iron carbide has been referred to by some asdispersion of the cementite.

In order to arrive at fine grain size (including abnormality) it has.been common to add, in the furnace ladle or in the molds, about onepound of aluminum per ton of steel. It has been discovered that ifvanadium be used as one of the shallow hardening elements, the amount ofaluminum may be materially reduced. Vanadium tends to produce fine grainstructure and shallow hardening in steel over a relatively widetemperature range in the hardening operation.

The alloy steels forming the subject matter of this invention arecharacterized by a high degree of ductility, toughness, resiliency andresistance to shock and fatigue.

As is well known, silicon is used in the manufacture of allow qualitysteels for the purpose of combining with the oxygen and thereby removingsaid oxygen. An excess of silicon always appears in the finished steelof this type and may properly be considered to be a trace of impurity.According to the appended claims such silicon will be included under theterm traces of impurities."

Though certain preferred analyses and steps have been recited in theforegoing specification, many modifications will occur to those skilledin the art. It is intended to cover all such modifications that fallwithin the scope of the appended claims. 1

What is claimed isl. A shallow hardening alloy steel which is composedof the following ingredients substantially in the amounts specified:

Per cent Carbon from .85 to .95 Manganese from .20 to .50 Chromium from.20 to .50 Vanadium from .075 to .20

Per cent Carbon from .45 to 1 Manganese from .40 to 1.25 Chromiumfrom--- an appreciable amount to .75 Vanadium from .075 to .20

remainder iron with traces of impurities.

WALTHER MATHESIUS. MARCUS A. GROSSMANN.

CERTIFICATE OF CORRECTION.

April 1 19 9.

. WALTHER MAIHEsIUs, ET AL. It is hereby certified that error appears inthe printed specification of the above numbered patent requiringcorrection as follows: Page 2, second column, line 26, for "95" read.95; page 5, first column, line 57, for the Word "allow" read alloyyendthat the said Letters Patent should be read Patent No. 2,155,5149.

with this correction therein that the same may conform to the record ofthe case in the Patent Office.

Signed and sealed this 15th day of June, .A. D. 1939.

(Seal) Acting Commissionerof, Patents.

